98 outback battery change.rear hatch won't open now.?????

I changed the battery in my 98 subaru legacy outback wagon.2.5 all wheel drive.It runs great for 300 thousand plus miles.I pushed the button under the dash and everything went back to normal except the back hatch.Car came with 3 sets of keys.It doesn't have the key fob with buttons.Just 3 keys and they fit the ignition and all the doors except the hatch.It happened once before and subaru mechanic fixed it after changing struts but i don't know what he did and he is on vacation for two weeks.Anyone know of a solution?.I'm stumped in Maine.